With the introduction of BOARDSDIR external boards can re-use common
code of BOARDS present in RIOTBASE. To be able to do this file
references may not use $(BOARD) since BOARD will be set by the
external BOARD.
cpu/$(CPU)/Makefile.features and cpu/$(CPU)/Makefile.dep are
automatically included
Part of moving CPU/CPU_MODEL definition to Makefile.features to have it
available before Makefile.include.
FLASHER and FFLAGS are evaluated by the main Makefile.include or by file
included by it. Their value does not need to be exported.
This will also prevent evaluating 'PORT' for FFLAGS when not needed.
Testing
-------
`git diff --word-diff` only reports `export` being removed.
`git show --stat` reports `84 insertions(+), 84 deletions(-)`
Which is the same amount as lines that where matching
`export[[:blank::]]\+VARIABLE`.
We have sane defaults for `ELFFILE` and `HEXFILE` in the root
`Makefile.include`. The local definition for `ELFFILE` of mbed_lpc1768's
`Makefile.include` was wrong, which caused e.g. `make buildsize` to
fail.
Creating all object files in one directory is bound to produce name
clashes. RIOT developers may take care to use unique file names, but
external packages surely don't.
With this change all the objects of a module (e.g. `shell`) will be
created in `bin/$(BOARD)/$(MODULE)`.
I compared the final linker command before and after the change. The
`.o` files (e.g. `startup.o`, `syscall.o` ...) are included in the same
order. Neglecting the changed path name where the `.o` files reside, the
linker command stays exactly the same.
A major problem could be third party boards, because the location of the
`startup.o` needs to the specified now in
`boards/$(BOARD)/Makefile.include`, e.g.
```Makefile
export UNDEF += $(BINDIR)msp430_common/startup.o
```
An application might want to use C11 features. The user would assume
that setting `CFLAGS=-std=gnu11` in the Makefile would work. It does not
since the board's Makefile.include shadows the `-std` flag.
This patch removes the `-std=gnu99` from the various Makefile.includes,
and sets the flag in the common Makefile.include of RIOT instead.
If an `-std` flag was provided by an earlier Makefile (the application,
the board, or the CPU [whilst only the former one should]), then no
additional flag is set. It is first tested if the supplied compiler
understands `-std=gnu99`, then `-std=c99`.
